Security of personal information is gaining greater importance in recent years. Biometrics authentication is attracting attention as individual authentication technology for ensuring security. Biometrics authentication is authentication technology that uses physiological information of a person, and is excellent in terms of convenience and preservation of confidentiality.
Examples of known conventional biometrics authentication technology include authentication using a fingerprint, iris, voice, face, or vein on the back of a hand or on the palm side of a finger. In vein biometric authentication, in particular, a user only has to present a part of his/her body such as a hand or a finger to an authentication device for authentication. Vein biometric authentication (i.e., vein authentication devices) therefore causes less reluctance in users. Furthermore, utilizing in vivo information, vein authentication devices are highly fraud-proof.
The description given below focuses on finger vein authentication devices.
A finger vein authentication device first irradiates a finger with infrared light, which is scattered inside the finger and then transmitted to the outside. The finger vein authentication device picks up the infrared light transmitted through the palm side of the finger.
Since hemoglobin in blood absorbs infrared light more than its surrounding tissues, the image picked up by the finger vein authentication device is a visualization of blood vessels running under the skin on the palm side of the finger (i.e., finger veins) as a dark shadow pattern (i.e., finger vein pattern).
Features of the finger vein pattern are registered in the finger vein authentication device in advance.
For authentication, the finger vein authentication device picks up an image of the user's finger. The finger vein authentication device accomplishes individual authentication by obtaining a correlation between a finger vein pattern of the image picked up and the features registered in advance.
However, conventional finger vein authentication devices pick up an image of a finger inserted into the finger vein authentication devices. Therefore, users feel reluctant to insert a finger into the closed interior space of a finger vein authentication device.
A finger vein authentication device described in JP 2004-265269 A addresses this problem. This finger vein authentication device places a light source for irradiating a finger with infrared light on each side of a finger. A user can thus be authenticated by merely putting his/her finger on the device.
A drawback of this finger vein authentication device, which requires spaces flanking a finger to install the light sources, is that the device cannot be reduced in size.
WO 2002/099393 describes a flat-structured finger vein authentication device.
This finger vein authentication device has a light source set on the same plane as an image pickup device with respect to veins to be photographed.